Composition Analysis And Chromogenic Mechanism Of Turquoise From Maanshan,Anhui Province

Natural turquoises from Ma'anshan,Anhui is studied in this investigation.There is a research on Spectral characteristics,chemical composition,and coloration of turquoises from Ma'anshan through the methods which contained Infrared spectroscopy,Raman spectroscopy,optical fiber spectrometer,XRF,LA-ICP-MS,differential thermal analysis,chemical gas adsorption methods.The focus is on the characteristics of trace elements and REE partition of Ma'anshan turquoise,and compared the composition characteristics of turquoise from other places in China.In addition,the color genesis and characteristics of Ma'anshan turquoise samples are discussed and analyzed.The infrared spectrum of the turquoises from Ma'anshan are resulted mainly from the vibration mode and the frequency of water,hydroxyl units and[PO4]tetrahedron.According to the difference in the ratio of the absorption intensity between the infrared absorption peaks at783cm^-1 and 837cm^-1(0.81?0.93),it can provide a reference for distinguishing from other regions.The results of differential thermal analysis reveal that the water content of turquoises from Ma'anshan is about 20%,the structural water is lost at 248?406?,new phases(Aluminum phosphate with phosphorus quartz structure)are formed at 810?in which the structure of turquoise from Ma'anshan is destroyed.The trace elements and REE partition reveal that the contents of trace elements such as Zn,Co,Cr,and V in different colors of turquoise in Ma'anshan have certain differences.The blue sample contains a higher content of Cr,while the green sample contains a higher content of Zn,V,and Co.Compared with other origins,the turquoises from Ma'anshan are characterized by low barium and depleted uranium,and the content of Ba and U is lower than that of the turquoise metallogenic belt in the eastern section of Qinling.The content of Sr is similar to Shiyan and Baihe,and slightly higher than that of Tongling,far lower than Luonan,Xichuan,Hami and other places.Besides these,turquoises from Ma'anshan have higher Co content than Zhushan and Hami,but lower Cr and V content.The Co/Ni ratio of pyrite in the sample wall rock is about 1.98-9.28,indicating that it is of low-temperature hydrothermal origin,which to some extent indicates the origin of the Ma'anshan turquoise deposit.In addition,the total REE changes of Ma'anshan turquoise are different and content lower total,and the overall REE distribution curve is lower right,showing the characteristics of relatively rich LREE.Most samples show weak Ce and Eu negative abnormalities.Compared with other domestic production areas,the turquoise from Ma'anshan can be distinguished from Hubei turquoise which has no obvious differentiation between LREE and HREE,showing obvious positive Eu anomalies and Ce negative anomalies from Hubei;the turquoise from Ma'anshan can be constrasted with the turquoise which characteristic of HREE enrichment and the strong Eu anomaly in Baihe.The turquoise's color from Ma'anshan is mainly caused by the d-d electronic transition of Cu²⁺and Fe³⁺,and the color is mainly blue to green,the hue angle varies from 167 to 221°,C^*varies from 19 to 35,and L^*varies from 73 to 94.The pores of different colors of turquoise have certain differences.The smaller the pore volume of the same color turquoise,the higher the C^*of the sample,and the opposite of the change of L^*.The hue of the blue turquoise is basically unchanged after being soaked in water,and the hue of the green sample changed from green to yellow;at the same time,the C^*and L^*of the turquoise after soaking in water decreased to varying degrees.